The present invention relates to data communications. More specifically, it relates to the transmission of packets in a point to point communication link.
Connection oriented point-to-point communication links, such as a Layer 2 Tunneling Protocol (L2TP) tunnel, are an increasingly common feature of network infrastructures. Tunnels are prearranged connections established by agreement between internet service providers (ISPs). See Request for Comment (RFC) 2661 and Layer Two Tunnelling Protocol (L2TP), A. Valencia, et al., draft-ietf-pppext-12tp-16.txt, June 1999, herein incorporated by reference, available from the Internet Engineering Task Force (IETF) at www.ietf.org for more information. FIG. 1 shows an architecture 10 that illustrates two L2TP tunnels 56 and 58 from tunnel initiators 30 and 40, respectively, established through a public IP network 70 to a tunnel endpoint server 50.
An L2TP tunnel typically provides a conduit for communications between client devices served by the tunnel initiators and a server device served by tunnel endpoint 50. Typically, a single tunnel slot provides the communication link between a client and server.
When a client device establishes a dial-up connection with a tunnel initiator (TI) 30 or 40, then the TI typically recognizes the client device as a tunnel client by means of an authentication protocol, such as RADIUS, see Request For Comment (RFC) 2138, herein incorporated by reference, or by other means for identifying the client, such as through the use of a mobile identification number (MIN) in mobile applications or, for protocols not directed toward mobile applications, the use of a Dial-up Number Information Service (DNIS) or Automatic Number identification (ANI). The authentication process can be adapted to provide an address for a tunnel endpoint device for the client. Alternatively, the client device itself may provide the tunnel endpoint address. In still another approach, each TI may have a pre-constructed table containing entries that associate a client device identifiers with a tunnel endpoint address value.
Independent of how the tunnel endpoint address is obtained, the tunnel initiator will establish a tunnel connection to the tunnel endpoint device.
Tunnel endpoint devices are typically stand-alone devices that operate independently of other tunnel endpoints. As a result, the tunnel endpoint devices are difficult to scale in order to cope with high levels of traffic to a server device connected to the tunnel endpoint device. In addition, with a single tunnel endpoint device serving a given server device, failure of the tunnel endpoint device can block all traffic to the server.
Thus, the need remains for a method for providing multiple tunnel endpoint devices that can serve a single server device.
In accordance with preferred embodiments of the present invention, some of the problems associated with combining multiple tunnel endpoint devices are overcome.
An embodiment of a system, according to the present invention, for terminating tunnel connections includes a first network and a plurality of network devices. Each network device has a network interface coupled to the first network and has a local address that is unique on the first network. Each network device is configured to receive a connection request message having a source address field, a destination address field, and a source tunnel identification field and, responsive thereto, construct a connection reply message having a source address field set to the local address of the network device, a destination address field set to the value of the source address field of the connection request message, a source tunnel identification field set to a value selected by the network device, and a destination tunnel identification field set to the value of the source tunnel identification. The connection reply message then being transmitted onto the first network. A master network device has a first interface coupled to the first network and a second interface for communicating with a second network. The master network device also has a first global address that is unique on the second network. The master network device is configured to receive tunnel connection request messages having the first global address in the destination field from the second network and, for each connection request message received, select one of the plurality of network devices, insert the local address for the selected network device into the destination field of the received connection request message, and forward the received connection request message to the selected network device over the first network. A network address translation device has a first network interface coupled to the first network and a second network interface for communicating with the second network. The network address translation device also has a second global address that is unique on the second network. The network address translation device is configured to receive the connection reply messages and, responsive thereto, create a table entry for each connection reply message that includes the value of the destination address field and the value of the source address field for the received connection reply message. The network address translation device is also configured to insert the second global address into the source address field of the connection reply message and transmit the connection reply message onto the second network.
Another embodiment of a system for terminating tunnel connections, according to the present invention, includes a first network along with a plurality of network devices, each network device having a first network interface coupled to the first network and having a local address that is unique on the first network. Each network device also has a second network interface for communicating with a second network and has a global address that is unique on the second network. Each network device is configured to receive a connection request message on the first network interface having a source address field, a destination address field, and a source tunnel identification field and, responsive thereto, construct a connection reply message having a source address field set to the global address of the network device, a destination address field set to the value of the source address field of the connection request message, a source tunnel identification field set to a value selected by the network device, and a destination tunnel identification field set to the value of the source tunnel identification field of the connection request message. Each network device is further configured to transmit the connection reply message over the second network interface onto the second network. A master network device has a first interface coupled to the first network and a second interface for communicating with the second network. The master network device has a master global address that is unique on the second network. The master network device is configured to receive tunnel connection request messages having the master global address in the destination field from the second network and, for each connection request message received, select one of the plurality of network devices, insert the local address for the selected network device into the destination address field of the received connection request message, and transmit the received connection request message as modified over the first network interface onto the first network.
An embodiment of a method for terminating tunnel connections, according to the present invention, calls for transmitting a tunnel connection set-up request from a first network device having a first global address value to a second global address value, the tunnel connection set-up request including a source address field containing the first global address value, a source tunnel identifier field containing a first tunnel identifier value assigned by the first network device, and a destination address field containing the second global address value. The method also calls for receiving the tunnel connection set-up request at a second network device corresponding to the second global address value, selecting one of a plurality of tunnel endpoint servers coupled to the second network device, and forwarding the tunnel connection set-up request to the selected tunnel endpoint server. Upon receiving the tunnel connection set-up request in the selected tunnel endpoint server, the method sets forth forming a tunnel set-up reply by inserting the value from the source address field of the tunnel set-up request into a destination address field of the tunnel set-up reply, inserting the value from the source tunnel identifier field of the tunnel set-up request into a destination tunnel identifier field of the tunnel set-up reply, selecting a second tunnel identifier value for the tunnel connection, inserting the second tunnel identifier value into a source tunnel identifier field of the tunnel set-up reply, and inserting an address value for the selected tunnel endpoint server into a source address field of the tunnel set-up reply. The method then provides for transmitting the tunnel set-up reply to the first network device over the first network.